Absorbent articles such as disposable diapers, incontinence pads, training pants, and catamenial napkins generally include an absorbent core for receiving and holding body exudates. The absorbent core typically includes a fibrous web, which can be a nonwoven, airlaid web of natural or synthetic fibers, or combinations thereof. Fibrous webs used in such absorbent articles also often include certain absorbent gelling materials usually referred to as "hydrogels," "superabsorbent" or "hydrocolloid" materials to store large quantities of the discharged body fluids. These materials absorb through capillary or osmotic forces, or a combination of both.
Alternative absorbent materials capable of providing capillary fluid transport are open-celled polymeric foams. If made appropriately open-celled polymeric foams provide features of capillary fluid acquisition, transport, and storage required for use in high performance absorbent cores for absorbent articles such as diapers. Absorbent articles containing such foams may also possess desirable wet integrity, provide suitable fit throughout the entire period the article is worn, and may avoid changes in shape during use. In addition, absorbent articles containing such absorbent foam structures could be easier to manufacture on a commercial scale. For example, absorbent foam diaper cores could simply be stamped out of continuous foam sheets and could be designed to have considerably greater integrity and uniformity than air-laid fibrous absorbent cores containing particulate absorbent gelling materials.
Besides absorbency and manufacturing ease, another desirable property of open-celled polymeric foams is the ability to make shaped or contoured absorbent cores having various shape configurations, fluid absorbency properties, and wear characteristics. For example, shaped or contoured absorbent cores made from open-celled foam materials having particularly desirable fluid transport characteristics are disclosed in U.S. Pat. No. 5,147,345 ('345 patent) issued to Young et al. on issued Sep. 15, 1992 and hereby incorporated herein by reference. The Young et al. '345 absorbent core comprises a fluid acquisition/distribution component that can be fibrous or foam based, as well as a fluid storage/redistribution component that comprises a hydrophilic, flexible, open-celled polymeric foam.
Forming shaped or contoured absorbent cores from foam materials, including those disclosed in Young et al. '345, is advantageous because the material is easily formed into webs that can be processed as rollstock. For example, the hourglass-shaped foam layer shown in FIGS. 2 and 9 of Young et al. '345 is typically made from web material that may be processed off of rollstock by notching, cutting, severing and otherwise shaping to form the hourglass-shaped piece. However, because each hourglass-shaped layer is cut from a single piece of material, it has substantially uniform material properties, and the absorptive characteristics of the layer are also substantially uniform. Therefore, fluid is absorbed from one layer to the next, from an acquisition layer to a storage layer, for example, if the absorbing layer capillary absorption pressure exceeds the desorption pressure of the donating layer. However, the use of an hourglass-shaped layer limits the overall efficiency of the absorbent core by placing material in areas where it may not be needed. For example, the acquisition layer may include material in the waist area where it is not typically needed, and the storage layer would include material in the crotch area where may not be desired. Also, in forming the hour-glass shapes, a significant amount of unusable foam scrap may be created.
Other absorbent materials, such as non-woven materials suitable for processing from rollstock, are also typically substantially uniform in nature. Therefore, although most materials easily processable from roll stock may be formed into shaped absorbent cores, the resulting absorbent cores have uniform material characteristics such as thickness and chemistry, resulting in uniform absorbent characteristics.
Accordingly, it would be desirable to be able to independently vary the material characteristics of an absorbent core in predetermined regions of an absorbent article, thereby varying the absorptive characteristics of the predetermined regions, but still be able to efficiently make the core from webs suitable for processing from rollstock in a manner that minimizes material use and scrap generation.
It would also be desirable to make an absorbent article with areas of the absorbent article subject to rapid fluid acquisition, such as the crotch area, tailored to provide rapid acquisition and distribution to other regions of the absorbent article tailored for fluid storage and/or redistribution.
It would be further advantageous to be able to independently vary all the material characteristics of various parts of an absorbent core, such as thickness, shape, and chemistry, thereby minimizing scrap while also providing for tailored absorbent characteristics, resulting in optimum fluid management and greater comfort to the wearer.